Bacteria are microscopic singel-celled organisms without a nucleus that are found in almost every environment. They reproduce rapidly by cell decision. They are primarily differentiated on the basis of their shape (spherical, rod or spiral shaped) but are now also classified by their genetics. Of the countless species of bacteria, it is presumes that only a fraction are known and have been researched.

The great majority of all bacteria species are harmless to humans and we even live in symbiosis with some species:We need intestinal bacteria for our digestions and we also have many harmless bacteria living on our skin and mucous membranes that protect us against invasion by pathogenic species.

Only a few bacteria species cause diseases in the human body when they enter the body and start to replicate. This opportunity presents itself particularly in immunocompromised people and as a result of major medical procedures. What is critical for preventing a bacterial infection is first preventing contamination. This means that stringent hygiene measures on hospital wards and also in the operating room that comply with the sterilisation and disinfection guidelines are of major importance.

Bacterial infections are primarily treated with antibiotics but sometimes the focus of the inflammation also has to be removed surgically. Some bacteria have developed immunity to certain antibiotics (resistance) over time. The spread of antibiotic resistance can be attributed to a special feature of bacteria:Most of their genetic material is present as a large chromosome but they also have short, ring-shapes genetic structures known as plasmides. A special characteristic of these plasmids is that thay can be exchanged among completely different species.

Antibiotic resistance genes are located primarily on plasmids and can therefore spread rapidly.

Multiresistant pathogens are bacteria that are resistant to several or even all available antibiotics. Infections with these pathogens can therefore be treated only with difficulty or not at all. Nosocomial infections are increasingly caused by resistant or multiresistant pathogens.

The increased and uncontrolled or incorrect use of antibiotics in humans and animals has led to an increase in the number of multiresistant bacteria. Multiresistant pathogens do not generally cause more frequent infections nor are such infections more aggressive. The danger is that if an infection develops, they are difficult to treat because most medications are ineffective.

In addition to MRSA, certain Klebsiella spp, enterococci and pseudomonads are also multiresistant pathogens.

ESBL stands for extended-spectrum beta-lactamase. Beta-lactamases are enzymes that open up beta-lactam rings and are therefore able to inactivate an important group of antibiotics, the beta-lactam antibiotics (e.g. cephalosporins). These antibiotics disrupt the structure of the bacterial cell wall.

ESBL become problemativ if the ability to produce this enzym is transferred to Gram-negative rod-shaped members of the Enterobacteriaceae family. These bacteria (e.g. E.coli, Klebsiella soo and Proteus spp) live in the intestines of healthy people but are also ingested from the environment and are important for the functioning of the intestinal flora. If they obtain the ability to form ESBL from the environment, this is not dangerous in and of itself. It becomes a problem when the ESBL bacteria - in mechanically ventilated or immunocompromised patients, for instance- replicate in the mucous membrane of the large intestine or the urinary or respiratory tract and cause pathological symptoms. This can lead to infections of the urinary tract that are difficult to treat, lung inflammations that heal poorly or wound healing disorders in which wounds suppurate and emit a strong odour of putrefaction.

ESBL-producing bacteria are resistant to an entire range of antibiotics and often only certain reserve antibiotics remain as a treatment option, primarily carbapenems with the antibiotic colistin often being the last option.

MRSA bacteria are staphylococci that are resistance to the antibiotic methicilin. Staphylococci are naturally present on the skin and the mucous membranes and they play an important role in nosocomial infections in particular.

Many of MRSA strains are resistant not only to beta-lactam antibiotics (such as methicilin) but also to other types of antibiotics, meaning that they are multiresistant.

Their name is derived from the fact that historically, susceptibility testing was carried out using the representative antibiotic methicilin.

Until the 1990s, MRSA strains were found almost exclusively in hospitals and became a problem in recent years primarily because they also developed resistance to other antibiotics as well (--> multiresistant germs). The glycopeptide antibiotics such as vancomycin are used to control MRSA strains.

For about 20 years, MRSA strains have also been found outside hospitals, making it necessary to differentiate between hospital-acquired (HA) and community-acquired (CA) MRSA. There is also livestock-associated (LA) MRSA that is the result of using antibiotics in animal husbandry.

Similar to MRSA, there are also antibiotic-resistant strains of the skin bacteria Staphylococcus epidermis. S. epidermis and other staphylococci form part of the completely normal skin and mucosal flora of humans and do not cause any diseases.

The antibiotic-resistant S. epidermis strains (MRSE) are also no danger to healthy people. If, however, they infect people with a weakened immune system - via implanted foreign bodies such as catheters, prostheses, artificial joints, pacemakers, heart valves and so on - treatment becomes difficult because antibiotics have no or little effect.

Enterococci - usually referring specifically to the intestinal bacterium Enterococcus faecium - are common pathogens that cause nosocomial infections, particularly in patients in intensive care units. At-risk patients are usually very ill, older patient with a weakened immune system. Enterococci are often multiresistant.

Vancomycin-resistant enterococci, the VRE bacteria, are particularly problematic. Because they are resistant to vancomycin, one of the reserve antibiotics, they are a feared nosocomial microorganism. They have often also developed resistance to a number of other antibiotics which leaves very few treatment options available.

Fig.: Development stages of a biofilm

Biofilms develop when microorganisms settle on surfaces. There they form communities in which the bacteria are surrounded by a matrix made up of water and biopolymers (polysaccharides, proteins, lipids and nucleic acids) that is formed by the microorganisms. This process can take weeks or even years and occurs in several stages.

Biofilms offer microorganisms protection from desiccation and toxic substances and enable them to survive periods without nutrients. In more than 60% of all bacterial infectious diseases, the pathogens protect themselves by forming biofilms because the mucous-like matrix formed by the bacteria is very difficult for immune cells and active substances to penetrate. Bacteria in biofilms also greatly slow down their metabolism and their growth rate. Antibiotics are only effective against metabolically active, rapidly growing bacteria, however.

Depending on the level of activity, cells can also constantly detach from the biofilm. This can lead to chronic or recurrent infections, for example. Effective control is usually only possible at an early stage of biofilm development. Due to their reduced metabolic acitivity, pathogens that are present in biofilms are also difficult to culture using conventional methods and have therefore only been poorly investigated.

The metal or polymer surfaces of implants and medical devices that are left in the body for longer periods (catheters, artificial heart valves, shunts, etc.) provide particularly favourable conditions for the formation of biofilms. About half of all nosocomial infections are the result of surgical implants.

Heraeus Medical

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